CN106716148B - Voltage sensing device - Google Patents
Voltage sensing device Download PDFInfo
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- CN106716148B CN106716148B CN201580052763.3A CN201580052763A CN106716148B CN 106716148 B CN106716148 B CN 106716148B CN 201580052763 A CN201580052763 A CN 201580052763A CN 106716148 B CN106716148 B CN 106716148B
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- sensing device
- electrode
- voltage sensing
- voltage
- carrying conductor
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R15/00—Details of measuring arrangements of the types provided for in groups G01R17/00 - G01R29/00, G01R33/00 - G01R33/26 or G01R35/00
- G01R15/04—Voltage dividers
- G01R15/06—Voltage dividers having reactive components, e.g. capacitive transformer
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R15/00—Details of measuring arrangements of the types provided for in groups G01R17/00 - G01R29/00, G01R33/00 - G01R33/26 or G01R35/00
- G01R15/14—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks
- G01R15/16—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks using capacitive devices
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
- G01R19/0084—Arrangements for measuring currents or voltages or for indicating presence or sign thereof measuring voltage only
Abstract
The invention relates to a voltage sensing device (1) for a high and/or medium voltage power carrying conductor (2), comprising: a radially outer electrode (3) operable as a first sensing electrode of a sensing capacitor for sensing a voltage of the power carrying conductor; a radially inner electrode (2,6) operable as a second sensing electrode of the sensing capacitor; a dielectric material (5) arranged between the inner electrode (2,6) and the outer electrode (3), wherein the coefficient of thermal expansion of the material of at least one electrode (3,2,6) is selected such that the material compensates for a temperature-dependent parameter of the dielectric material (5) and/or the other electrode (3,2,6) affecting the capacitance of the voltage sensing capacitor.
Description
The invention relates to a voltage sensing device for a high-voltage and/or medium-voltage carrying conductor. In particular, the present invention relates to a voltage sensing device for high and/or medium voltage carrying conductors, such as cables in an electrical distribution network. The invention also relates to a cable connector according to the invention that can be used with a sensor, and to a cable accessory according to the invention comprising a sensor.
Operators of the power network use voltage and current sensors to monitor the status of the power network at the installation location of the sensors and on the various cables. An embodiment of a high voltage capacitor suitable for measuring the voltage of an overhead power line is disclosed in US 4,963,819. The capacitor dielectric is placed directly on the power line conductor, which acts as one electrode of the capacitor. The other electrode of the capacitor is placed on the outer surface of the dielectric and is protected on each side by a guard ring. Stress control is provided between the outer capacitor electrode and the guard ring and also at the outer edge of the guard ring. The capacitor may be enclosed in a grounded enclosure, which may contain one or more current transformers.
US 2006/020671 a1 discloses a voltage sensor having a primary capacitance and a secondary capacitance molded as a voltage divider of a solid dielectric material. The capacitance is preferably constructed by coating and made of the same material or at least a material with almost the same temperature coefficient of the dielectric constant.
WO 2012/052584 a1 discloses a voltage measuring device comprising an element that configures the electric field between the power carrying conductor and the structure. The element configuring the electric field comprises a body of insulating material having dielectric properties unaffected by temperature variations.
And finally DE 2413927 a1 discloses a high-voltage capacitor suitable for measuring the voltage of a power line. The system includes an auxiliary capacitor as part of an evaluation device that generates a signal corresponding to a change in capacitance of the auxiliary capacitor resulting from an external influence.
EP 0869369 a2 discloses a capacitive voltage divider for high voltage environments. The capacitive voltage divider comprises a correction device for compensating for temperature-dependent behavior of components of the voltage divider. The correction device effectively compensates for temperature-dependent behavior based on data of the experiments performed.
According to the prior art, there is still a need to provide a voltage sensing device for high and/or medium voltage power carrying conductors, which is simple and yet cost-effective to produce and provides a certain amount of accuracy.
The present invention solves this problem. The invention provides a voltage sensing device for a high and/or medium voltage power carrying conductor, the voltage sensing device comprising:
-a radially outer electrode operable as a first sensing electrode of a sensing capacitor for sensing a voltage of the power carrying conductor;
-a radially inner electrode operable as a second sensing electrode of the sensing capacitor;
a dielectric material arranged between the inner electrode and the outer electrode,
wherein the coefficient of thermal expansion of the material of at least one of the electrodes is selected such that the material compensates for a temperature-dependent parameter of the dielectric material and/or other electrodes affecting the capacitance of the voltage sensing capacitor.
Generally, a voltage sensing device according to the present invention may be included in a capacitive voltage sensor assembly. The radially outer electrode, the radially inner electrode, and the dielectric material disposed between the electrodes may operate as a sensing capacitor. The sensing capacitor may be included in the voltage sensor assembly. The voltage sensor assembly may also include a secondary capacitor. The sensing capacitor and the secondary capacitor may be connected in series to form a capacitive voltage divider. A capacitive voltage divider is operable to sense the voltage of an inner conductor such as a power cable or a cable connector or a power carrying conductor such as a bus bar. The sensing capacitor according to the invention may also be used in other known circuits, for example as an electrical decoupling element of an operational amplifier (OP AMP).
In operation, components of the voltage sensor assembly are heated due to the current flowing through the power carrying conductor. Typical temperature ranges may be between-10 ℃ and +90 ℃ or more. As a result of these temperature changes, the materials used for the voltage sensing devices can change their dimensions and other characteristics, such as relative dielectric constant. The materials may stretch and/or their relative dielectric constant may change when the materials are heated. This change in size and/or relative permittivity affects the capacitance of the sensing capacitor, which tends to have a non-negligible temperature gradient.
For example, the temperature dependence of the capacitance can be calculated by the following formula (valid only for cylindrical shaped capacitors; if other forms of capacitors are used, the corresponding formula needs to be used):
C＝2πε0εrel*llnRoutRin
wherein
C: is the capacitance of the sensing capacitor
εrel: is the relative permittivity of the dielectric material between two electrodes
l: is sensing the length of the capacitor
Rout: is the radius of the radially outer electrode of the sensing capacitor
Rin: is the radius of the radially inner electrode of the sensing capacitor
εrel、l、RoutAnd RinMay be temperature dependent.
The temperature dependence described above can lead to a loss of accuracy of the voltage sensor assembly with changing temperature. The present invention seeks to solve this problem by selecting the material of at least one electrode of the voltage sensing device such that it compensates for the temperature-dependent behavior or parameter of the other electrodes and/or the dielectric material. In other words, by choosing for example a material for the radially outer electrode which for example maintains the geometry of the radially outer electrode within the above mentioned temperature range, it is possible to inhibit the distance between the inner electrode and the outer electrode from changing with temperature. With such embodiments, the dielectric material may be maintained within the boundaries of the outer electrode even as the temperature changes, and in turn, maintain a substantially constant distance to the inner electrode. Another way to explain the principle of the invention is that the radially outer electrode needs to fulfill the following two requirements:
a) in order to be operable as a sensing electrode of the sensing capacitor, the radially outer electrode needs to be conductive; and is
b) The radially outer electrode needs to be mechanically or geometrically stable with changing temperatures in the above mentioned temperature range, or at least the radially outer electrode needs to be sufficiently stable to inhibit stretching of the dielectric material.
It is also possible to influence the capacitance of the voltage sensing device by choosing a suitable material for the inner electrodes. When the dielectric material is firmly fixed to either the radially inner electrode and/or the radially outer electrode, for example, the expansion toward the voltage sensing device side (e.g., the opening between the radially outer electrode and the radially inner electrode) may be inhibited or suppressed. This may be achieved, for example, by a sufficiently large static friction between the electrode or electrodes and the dielectric material or by using a suitable binder or adhesive between the dielectric material and the electrode or electrodes.
An additional way of optimizing the accuracy of the voltage sensing device is to also take into account the temperature dependence of the dielectric coefficient of the dielectric material when selecting the material for the inner or outer electrode.
The radially outer electrode may comprise any kind of electrically conductive material capable of fulfilling the requirements of claim 1, the coefficient of thermal expansion of the material of the outer electrode having to be selected according to the requirements of claim 1 such that the material compensates for the temperature dependent behavior of the other electrode and/or the dielectric material. It is also possible that the radially outer electrode comprises a non-conductive core part coated with a conductive material. It is advantageous for the invention if the tensile modulus of the radially outer electrode is significantly higher than the elastic modulus of the dielectric material. With such a configuration, the size of the radially outer electrode is not affected by any stretching due to the temperature rise of the dielectric material. Examples for such materials are boron nitride, aluminum, copper, steel and/or alloys comprising any of these materials. The electrode may also include a conductive polymer.
The radially outer electrode may extend at least partially around the power carrying conductor in such a way that: the inner surface of the radially outer electrode faces the radially inner conductor. The outer electrode may comprise a cylindrical shape if it extends entirely around the power carrying conductor. In other words, the outer electrode may have a flat profile in an axial longitudinal sectional view of the voltage sensing device, such that all parts of the inner surface of the outer electrode are radially equally close to the central axis of the power carrying conductor. A flat profile may be advantageous for keeping the overall size of the voltage sensing device small and may be particularly cost-effective to manufacture. All other shapes are possible, ideally depending on the shape of the power carrying conductor, such as for example a square or rectangular shape or a sector. If the radially outer electrode does not extend entirely around the power carrying conductor, additional means for holding the electrode in its position with respect to the radially inner electrode need to be arranged within the voltage sensing device.
Independently of other features, the radial thickness of the radially outer electrode may be between 1mm and 6mm, preferably between 1mm and 3mm, depending on the material used.
The radially inner electrode may comprise any kind of electrically conductive material capable of fulfilling the requirements of claim 1, the coefficient of thermal expansion of the material of at least one electrode having to be selected according to the requirements of claim 1 such that the material compensates for the temperature dependent behavior or parameter of the other electrode and/or the dielectric material. Examples for such materials are copper, steel, nickel, aluminum or alloys comprising any of these materials. It is also possible that the radially inner electrode comprises a non-conductive core portion coated with a conductive material. The electrode may also include a conductive polymer.
The radially inner electrode may either be the power carrying conductor itself, or it may be an additional element extending at least partially around the power carrying conductor in such a way that: the outer surface of which faces the radially outer electrode. The additional element may comprise a cylindrical shape if the additional element extends entirely around the power carrying conductor. In other words, the radially inner electrode may have a flat profile in an axial longitudinal sectional view of the voltage sensing device, such that all parts of the inner surface of the radially inner electrode are radially equally close to the central axis of the power carrying conductor. A flat profile may be advantageous for keeping the overall size of the voltage sensing device small, and may be particularly cost-effective to manufacture. All other shapes are also possible, such as for example the shapes listed above for the radially outer electrode.
In the case where the conductor is an inner electrode, the thickness of the inner electrode may be as high as the diameter of the electrode. The individual inner electrodes have a thickness of 0.5mm to 3mm, preferably 1mm to 2 mm.
The two electrodes may comprise the same axial length and/or may be arranged in the same axial position. It is also possible that the two electrodes are different in length and/or have different axial positions relative to each other. One embodiment according to the invention is a radially inner electrode that is longer in the axial direction as the radially outer electrode. They may be mutually centred so that the radially inner electrode extends over both ends of the outer electrode. The two electrodes may be arranged in a symmetrical manner with respect to each other.
The dielectric material arranged between the inner and outer electrodes may be any material having dielectric properties such as, for example, silicone, polyurethane, high modulus ethylene propylene rubber), cross-linked polyethylene or epoxy. Due to the inventive idea it is even possible to choose a material for the dielectric material with a high coefficient of thermal expansion, since this characteristic will be compensated by the temperature dependent behavior or parametric behavior of the at least one electrode. This provides the possibility of selecting a material with a reasonable price. The radial thickness of the dielectric material depends on the material used and may for example be between 6mm and 14 mm.
The power carrying conductor may be a cable connector, such as a cable connector for medium or high voltage power cables. The cable connector may be adapted to receive an inner conductor of a power cable. It may be adapted to mate with an electrical power carrying cable, for example, releasably or permanently, or it may be adapted to mate with a cable adapter attached to the electrical power carrying cable. The cable connector may be at least partially electrically conductive. It may comprise a conductive surface or a conductive surface portion. According to the invention the cable connector may comprise a receiving portion for receiving a portion of the voltage sensing device, e.g. the radially inner electrode and/or a portion of the contact element arranged between the radially inner electrode and the power carrying conductor.
The power carrying conductor may also be a bus bar. The bus bar may have a rectangular cross section.
The voltage sensing device according to the invention having a radially inner electrode, a radially outer electrode and a dielectric material between the radially inner and outer electrodes may have a tubular shape. In other words, it may have a channel extending through the voltage sensing device. The tubular shaped voltage sensing device may have a hollow cylindrical shape. It may have an annular shape, i.e. the shape of a short tube. The sensing device may have a bent or twisted tube shape. The voltage sensing device may have a rectangular shape. As already explained above, the voltage sensing device according to the invention may extend either completely around the power conductor, or it may extend partially around the power carrying conductor.
According to one embodiment of the invention, the radially inner electrode comprises a portion of the power carrying conductor. In other words, the power carrying conductor may operate as a radially inner electrode, and the sensing capacitor according to the invention comprises the radially outer electrode, the radially inner electrode being the power carrying conductor itself and the dielectric material. This embodiment is very cost-effective because only two accessory components (e.g. the radially outer electrode and the dielectric material between the radially outer electrode and the power carrying conductor) are required in addition to the power carrying conductor to build the voltage sensing capacitor. Thus, the power carrying conductor fulfils two purposes, one being used as a conductor and one as an electrode of a capacitor.
In this embodiment, the material of the radially outer electrode needs to be selected to compensate for the temperature dependence of the relative dielectric constant of the dielectric material and/or the temperature dependence of the coefficient of thermal expansion of the power carrying conductor.
According to another embodiment, the inner electrode comprises a separate electrode element electrically connected to the power carrying conductor, the separate electrode element being placed between the power carrying conductor and the radially outer electrode. By this embodiment, a system can be provided which is independent of the thermal behaviour of the power carrying conductor. In such a system, it may be easier to adapt the materials to each other, so that the temperature dependence may be compensated for. Thus, such a system may provide even higher accuracy compared to previously described systems.
According to another embodiment, either or both electrodes may be arranged around the power carrying conductor. For such a configuration, the two electrodes may include a channel that may receive a power carrying conductor. The axial channel may be adapted to the shape of the power carrying conductor, e.g. the axial channel may for example comprise a rectangular, triangular or any angular, elliptical, oval or spherical or circular cross section.
According to another embodiment, the coefficients of thermal expansion of the materials of the radially outer and radially inner electrodes are selected such that the materials compensate for temperature-dependent parameters of the dielectric material and/or other electrodes affecting the capacitance of the voltage sensing device. As already indicated above, byrel、Rout、RinThe temperature dependence of and gives the temperature dependence of the capacitance. EpsilonrelIs due to the density that decreases with the temperature of the dielectric material. Rout、RinThe temperature dependence of and is due to thermal expansion of the electrode material. By selecting the materials of the radially outer and radially inner electrodes, these dependencies can be influenced and even compensated if certain material combinations are selected. Even if a dielectric material with a high temperature dependence is selected, which tends to be more affordable than a dielectric material with a low temperature dependence, a high level of accuracy may be achieved. By using radially inner and outer electrode tuning or correction systems, more parameters can be selected and tuned, which makes it easier to provide a voltage sensing device with a relatively high accuracy by using a relatively cost-effective combination of materials.
According to another embodiment of the invention, the radially inner electrode and the radially outer electrode are made of the same material. If the materials of the radially outer and radially inner electrodes are chosen such that they are the same, the radially outer and radially inner electrodes behave the same as a temperature change, which leads to the fact that the distance between the electrodes remains substantially the same as a temperature change. Since the capacitance of the sensing capacitor depends only on erelThe dielectric coefficient of the dielectric material between the electrodes and the length of the l-sensing capacitor, so this contributes to higher accuracy. Such an embodiment may have cost-related advantages since a smaller number of different materials need to be handled during the production process.
According to another embodiment of the inventionThe radially inner electrode is made of a material having a higher coefficient of thermal expansion than the coefficient of thermal expansion of the material of the radially outer electrode. It is also possible to compensate for the parameter epsilon mentioned above if two different materials with two different coefficients of thermal expansion are chosenrelThe relative permittivity of the dielectric material between the electrodes and the length of the l-sensing capacitor. Thus, with varying temperature, this embodiment may provide even higher accuracy than the above-mentioned embodiment, in which both electrodes comprise the same material.
According to another embodiment, the contact element may be arranged between the power carrying conductor and the radially inner electrode. If the inner electrode is a separate electrode element arranged between the power carrying conductor and the radially outer electrode, it is necessary to electrically connect the inner electrode with the power carrying conductor. This may be done either by the inner electrode being a separate electrode element and directly contacting the power carrying conductor. Another possibility is to use an additional contact element arranged between the power carrying conductor and the radially inner electrode. Since the radially inner electrode is decoupled from the thermal expansion of the power carrying conductor, it is advantageous to provide an additional contact element between the conductor and the radially inner electrode. This may provide the possibility to build a sensing capacitor with a lower temperature correlation and again a higher accuracy.
Ideally, the contact element should be mechanically reliable and should withstand mechanical forces that may result from relative movement with respect to the power carrying conductor sensor. Mechanical forces that may originate from different thermal expansions of the radially inner electrode on the one hand and of the power carrying conductor on the other hand should also be tolerated. Such a contact element should also take up as little space as possible, so that the sensor can have a small size. The contact element may provide a short electrical path between the power carrying conductor and the radially inner electrode. The contact element may comprise an elastic portion which may provide an automatic contact between the power carrying conductors and may also compensate for different thermal expansions of the radially inner electrode and the power carrying conductors. The resilient portion may also provide sufficient contact pressure for reliable mechanical and electrical contact. The contact element may also be elastically supported or consist of an elastic material.
The contact element may comprise an elastomeric material. The elastomeric material may be electrically conductive, or the elastomeric material may have an electrically conductive surface. The elastomeric material may be disposed on an outer surface of the power carrying conductor, or on a surface of the inner electrode facing the power carrying conductor.
According to another embodiment of the invention, the voltage sensing device comprises at least one electrically grounded stress control element arranged adjacent to at least one edge of the radially outer electrode. Depending on the shape of the radially outer electrode and/or the radially inner electrode, the stress control element may comprise any of the above-described shapes of the radially outer electrode, e.g. it may be annular. It may extend entirely around the cable, or they may extend circumferentially partially around the cable. The stress control element may provide two benefits. One is to control and influence the electric field lines at the edges of the sensing capacitor, in particular the radially outer electrodes, so that the risk of breakdown between the electrodes is reduced.
According to another embodiment, the outer edge of the radially inner electrode and/or the radially outer electrode is shaped to minimize the strength of the electric field in the region. One possibility is to provide the edges of the electrodes with a rounded or curved shape. A curved profile may be advantageous in order to reduce the risk of electrical breakdown between the two electrodes. For example, a curved profile of the outer electrode taken along an axial longitudinal section of the sensor may be operable as geometric stress control. The curved shape may reduce the field concentration at the edge of the radially outer electrode. The same principle is true for the radially inner electrode. The edge of the radially inner electrode and/or the radially outer electrode may provide any known shape that reduces the risk of electrical breakdown, for example a shape according to the Rogowski profile. Applying this measure of bending to the outer and/or inner electrodes may allow the space between the electrodes to be reduced. This in turn saves space and makes the sensor smaller in size.
According to another embodiment of the invention, the voltage sensing device provides a printed circuit board having a low voltage capacitor disposed on and in electrical contact with the radially outer electrode. The electrical connection between the PCB and the radially outer electrode can be established in all known ways. The PCB may carry all known and suitable circuitry, such as for example a second capacitor (low voltage capacitor). The voltage sensing capacitor on the PCB and the second capacitor should be used as a voltage divider as mentioned above.
It is also possible that the voltage sensing device according to the invention provides a signal cable. The signal cable may or may not be in direct contact with the radially outer electrode and establish an electrical connection between the radially outer electrode and a PCB, which is to be arranged outside the high voltage environment and/or the medium voltage environment. According to another embodiment, it is also possible that the PCB is arranged on the radially outer electrode, as mentioned above, and that a signal cable connected to the PCB is used for transmitting the measured signal.
According to another embodiment, the voltage sensing device extends at least partially or entirely around the circumference of the power carrying conductor. The different possibilities relating to this embodiment have been described above. If it extends only partially around the circumference of the power carrying conductor, it may be necessary to provide additional means, as described above, for holding the radially outer electrode in position relative to the radially inner electrode.
The voltage sensing device may be integrated into a cable accessory such as, for example, a terminal, a connector, or a t-body. This constitutes a space-saving arrangement of the elements of the sensor. The voltage sensing device may further comprise two or more housings that are engageable with each other to form the voltage sensing device having a tubular shape. This may enable the voltage sensing device to be arranged around the power carrying conductor at a longer distance from one end of the power carrying conductor. The voltage sensing device may also comprise only a single piece and be mounted by being placed over the cable end.
The voltage sensing device may also be designed such that it can be easily attached and fixed to the cable termination. The connection between the cable terminal and the voltage sensing device needs to be designed such that an electrical connection between the end of the conductive cable and the radially inner electrode is established. The fixing may be performed by known mechanical elements, such as e.g. nuts or bolts, or by using a conductive adhesive.
The invention further comprises a cable connector for a high voltage power carrying conductor and/or a medium voltage power carrying conductor, the cable connector comprising an electrically conductive element adapted to electrically connect the cable connector to an electrode of the voltage sensing device described above.
The invention also relates to a cable accessory comprising the voltage sensing device described above.
The invention will now be described in more detail with reference to the following drawings, which illustrate specific embodiments of the invention:
FIG. 1 is a cross-sectional view of one embodiment of a voltage sensing device according to the present invention;
FIG. 2 is a cross-sectional view of another embodiment of a voltage sensing device according to the present invention;
FIG. 3 is a circuit diagram of a voltage sensing device according to the present invention;
FIG. 4 is a schematic cross-sectional view of a voltage sensing device according to the present invention integrated into a cable accessory;
FIG. 5 is a three-dimensional view of another embodiment of a voltage sensing device according to the present invention, an
Fig. 6 is a cross-sectional view of a signal cable of the voltage sensing device shown in fig. 4.
Various embodiments of the present invention are described herein below and illustrated in the accompanying drawings, wherein like elements have the same reference numerals.
Figure 1 shows a cross-sectional view along the longitudinal axis of a power carrying conductor 2 of an embodiment of a voltage sensing device 1 according to the invention. The power carrying conductor 2 is an inner power carrying conductor part of a high voltage cable and/or a medium voltage cable. The voltage sensing device 1 comprises a radially outer electrode 3, the radially outer electrode 3 being cylindrical in shape and comprising a channel 4 having a circular cross-section. Inside this channel 4, a dielectric material 5 of cylindrical shape is arranged. For example, the radially outer electrode 3 may be made of aluminum, copper or steel. For example, the dielectric material may be made of silicone rubber.
In order to provide a voltage sensing device 1 which can provide highly accurate measurement results, the dielectric material 5 may be attached to the radially outer electrode 3 using an adhesive or a tackifier. This helps to avoid bubbles in the electric field and to keep the dielectric material in place, as the changing temperature can affect the geometry of the components of the voltage sensing device.
If the dielectric material is silicone rubber, for example, which has no or only little adhesion to metal, a suitable adhesive that can be used is Scotch commercially available from 3M Germany, 3M Germany GmbH in Neuss, GermanyTM1619 silicone sealing material. For example, one way to attach the dielectric material to the radially outer electrode is to attach ScotchTM1619A silicone sealant material was applied to the inner surface of the radially outer electrode and Scotch was cured in an oven at about 60 deg.CTM1619 silicone sealant material for about 15 minutes or more. The dielectric material (e.g., silicone rubber) may then be molded or cast onto or into the prepared metal part. By using this particular sealing material, it is possible to create a continuously high adhesion between the radially outer electrode and the dielectric material that is higher than the tensile strength of silicone rubber. Other known tackifiers or adhesives may also be used.
Figure 2 shows a cross-sectional view along the longitudinal axis of a power carrying conductor 2 of another embodiment of a voltage sensing device 1 according to the invention. The power carrying conductor 2 may be a power carrying conductor of a high voltage cable and/or a medium voltage cable. The conductor 2 may also be a metal rod attached to the conductor of the cable. The voltage sensing device 1 comprises a radially outer electrode 3, the radially outer electrode 3 being cylindrical in shape and comprising a channel 4 having a circular cross-section. Inside this channel 4, a dielectric material 5 is also arranged in the shape of a cylinder. For example, the radially outer electrode 3 may be made of aluminum, copper or steel. For example, the dielectric material may be made of silicone rubber.
The embodiment shown in fig. 2 also provides a separate element between the power carrying conductor operable as the radially inner electrode 6 and the dielectric material, the radially inner electrode 6 being cylindrical in shape and comprising the channel 7. Within this channel 7, an electrical power carrying conductor 2 is arranged. The embodiment shown in fig. 2 also provides a contact element 8 arranged within the channel 7 and between the power carrying conductor 2 and the radially inner electrode 6. The contact element 8 electrically connects the power carrying conductor 2 with the radially inner electrode 6. The radially inner electrode may for example be made of aluminum, copper or steel and the contact element may for example be made of an electrically conductive silicone. Attaching the dielectric material to the radially inner electrode may use the same adhesive, tackifier or binder and the same process as described above with reference to fig. 1.
The embodiment shown in fig. 2 also provides a force control element 9 on each side of the radially outer electrode 3. The stress control element 9 may have an annular shape and may be made of aluminum, copper, steel or conductive paint or the same material as the radially outer electrode 3. The stress control element 9 may be used to inhibit stray fields in the region of the edge of the radially outer electrode.
The arrangement shown in fig. 1 or fig. 2 may be overmolded, for example, with a silicone material.
A possible arrangement of the voltage sensing device 1 shown in fig. 2 may provide a radially inner electrode made of aluminum overmolded by 8 silicone (for example, Powersil600) and a radially outer electrode made of aluminum. Another embodiment is a radially inner electrode made of 8mm silicone overmolded aluminum and a radially outer electrode of boron nitride. Another embodiment is a radially inner electrode made of 9mm silicone overmolded aluminum and a radially outer electrode made of brass CuZn 37. Yet another embodiment of the voltage sensing device 1 shown in figure 2 is a radially inner electrode made of 10mm silicone overmolded aluminum and a radially outer electrode made of stainless steel (e.g., 1.4878 or 1.4301). All other combinations of materials are also possible.
Fig. 3 is a circuit diagram of a voltage sensing device 1 according to the invention. The sensing capacitor 1 has a radially outer electrode 3 and a radially inner electrode 6. The radially inner electrode 6 is electrically connected to the power carrying conductor of the high voltage power network and/or the medium voltage power network via a contact element 8. The sensing capacitor 1 is electrically connected in series with the secondary capacitor 11 such that the sensing capacitor 1 and the secondary capacitor 11 can be operated as a capacitive voltage divider. The secondary capacitor 11 may be arranged on a Printed Circuit Board (PCB) element 12. The PCB element 12 may be arranged very close to the voltage sensing device 1 even in direct contact with the radially outer electrode 3. In this case, the electrical contact between the PCB element 12 and the radially outer electrode 3 may be formed via an exposed conductive area of the PCB element. Alternatively, the PCB element 12 may be arranged at a distance from the voltage sensing capacitor 1, and the PCB element 12 may be electrically connected to the radially outer electrode by e.g. a wire. One side of the secondary capacitor 11 is electrically connected to the voltage sensing capacitor 1 and the other side is electrically connected to ground.
Since the power carrying conductor 2 is electrically connected to the radially inner electrode 6 via the contact element 8, measuring the voltage of the power carrying conductor 2 can be done by measuring the voltage of the radially inner electrode 6. The voltage to ground of the radially inner electrode 6 of the sensing voltage sensing device 1 is measured by measuring the voltage across the secondary capacitor 11. The secondary capacitor is thus electrically connected to the measuring device 13 via the sensor conductor 14 and the ground conductor 15. The measuring device 13 is electrically connected in parallel to the secondary capacitor 11 via a sensor conductor 14 and a ground conductor 15. The measuring device 13 is electrically connected to ground via a conducting or semiconducting element 16.
In the capacitive voltage divider described above, the voltage of the power carrying conductor 2 is sensed by measuring the voltage across the secondary capacitor 11. Alternatively, the voltage of the power carrying conductor 2 may be sensed by measuring the current through the voltage sensing device 1.
Fig. 4 is a schematic cross-sectional view of a voltage sensing device 1 according to the invention integrated into a cable accessory 30. The cable accessory 30 comprises the power carrying conductor 2 and an isolation 31 with a skirt 32. The voltage sensing device 1 according to the invention integrated into the isolation 31 of the cable accessory may comprise all components described with reference to fig. 1 and/or fig. 2, all components being the sensing electrode 3, optionally two stress control elements 9 on both sides of the sensing electrode 3. The voltage sensing device 1 may also comprise a radially inner electrode, which may be either the power carrying conductor itself or a separate electrode element 6 as shown in fig. 2. The voltage sensing device 1 shown in fig. 4 further comprises an electrical connection (cable) 33 to electrically connect the voltage sensing device 1, for example, with a low voltage capacitance.
Figure 5 is a three-dimensional view of another embodiment of a voltage sensing device 1 according to the invention. This embodiment is used with a cable termination that provides the power carrying conductor 2 and an insulating layer 17 extending around the power carrying conductor.
The voltage sensing device 1 according to this embodiment comprises a radially inner electrode 6 and a radially outer electrode 3. A dielectric material 5 is arranged between the two electrodes 6 and the electrode 3. The two electrodes 6 and 3 may be made of the same material, which may be all the materials listed in the summary section of the description. The electrodes 6 and 3 may also be made of different materials or combinations of materials. The dielectric material 5 may be silicone or polyethylene or any other non-conductive material, such as those mentioned in the summary section of the description. It is possible to mold the dielectric material 5 between the two electrodes 6 and 3 and around the electrodes 6 and 3. It is also possible to fix the dielectric material to one or both electrodes by using any of the above mentioned adhesives, binders or adhesion promoters.
The radially inner electrode 6 is directly connected to the power carrying conductor 2 and may for example be shaped like an ear of the power carrying conductor 2. All other known shapes of the end of the power carrying conductor are also possible. The radially outer electrode 3 is electrically separated from the radially inner electrode 6 using a dielectric material 5. The dielectric material needs to provide a sufficiently high dielectric strength to withstand high and/or medium voltages.
The embodiment shown in fig. 5 is a voltage sensing device 1 extending only partially around a power carrying conductor. It is also possible to provide an equivalent embodiment that extends completely around the power carrying conductor as shown in fig. 5.
The radially outer electrode 3 may provide a printed circuit board (not shown in fig. 5) which is electrically connected to the radially outer electrode 3 and may include a low voltage capacitor. The low voltage capacitance of the voltage sensing device 1 and the PCB element 12 may be electrically connected to the circuit shown in fig. 3.
High voltage signal cables may be connected to the PCB components 12 to transmit measured data out of the high voltage area and to ground potential to the PCB components 12. It is also possible to electrically connect one end of the high voltage signal cable to the radially outer electrode 3 and the other end of the high voltage signal cable to a PCB which in this case will be located in a low voltage environment.
The electrodes are shaped with rounded edges in a specific high voltage manner to keep the electric field strength in the molded dielectric body below the limits of the materials used.
The high voltage signal cable is shown in cross-section in fig. 6. High voltage signal cables must be designed so that they can be used in high voltage environments. Thus, the high voltage signal cable provides a high voltage insulation 25 at its radial outer side. An electrically conductive wire mesh 24 at ground potential is placed under this insulation 25. An additional insulation 23 is foreseen under the metal screen and the conductor 22 is placed inside the additional insulation 23. The high voltage signal cable needs to be connected to the PCB element 12 and/or the radially outer electrode 3 in such a way as to withstand high and/or medium voltages.
A benefit of the voltage sensing device according to this embodiment is that it can be easily placed at the end of the cable without having to take away any insulation.
Claims (13)
1. A voltage sensing device (1) for a high and/or medium voltage power carrying conductor (2), the voltage sensing device comprising:
-a radially outer electrode (3) operable as a first sensing electrode of a sensing capacitor for sensing a voltage of the power carrying conductor;
-a radially inner electrode (2,6) operable as a second sensing electrode of the sensing capacitor;
-a dielectric material (5) arranged between the inner electrode (2,6) and the outer electrode (3),
wherein the coefficient of thermal expansion of the material of at least one electrode (3,2,6) is selected such that the material compensates for a temperature-dependent parameter of the dielectric material (5) and/or other electrodes (3,2,6) affecting the capacitance of the voltage sensing capacitor, and
the voltage sensing device further comprises a contact element (8) arranged between the power carrying conductor (2) and the radially inner electrode (6), the contact element comprising an elastic portion.
2. Voltage sensing device according to claim 1, wherein the inner electrode comprises a part of the power carrying conductor (2).
3. Voltage sensing device according to claim 1, wherein the inner electrode comprises a separate electrode element (6) placed between the power carrying conductor (2) and the radially outer electrode (3).
4. Voltage sensing device according to claim 1, wherein either or both electrodes (3,6) can be arranged around the power carrying conductor (2).
5. Voltage sensing device according to claim 1, wherein the radially inner electrode (2,6) is made of a material having a higher coefficient of thermal expansion than the coefficient of thermal expansion of the material of the radially outer electrode (3).
6. Voltage sensing device according to claim 1, comprising at least one ground stress control element (9) arranged adjacent to at least one edge of the radially outer electrode (3).
7. Voltage sensing device according to claim 1, wherein the outer edge of the radially inner electrode (6) and/or the radially outer electrode (3) is shaped to minimize the strength of the electric field in the region of the electrode edges.
8. Voltage sensing device according to claim 1, comprising a Printed Circuit Board (PCB) (12) with a low voltage capacitor (11) arranged on and in electrical contact with the radially outer electrode (3).
9. Voltage sensing device according to claim 1, comprising a signal cable (21) contacting the radially outer electrode (3) with a PCB.
10. Voltage sensing device according to claim 1, wherein the voltage sensing device (1) extends at least partially or entirely around a circumference of the power carrying conductor (2).
11. Voltage sensing device according to claim 1, wherein the voltage sensing device (1) is integrated into a cable accessory.
12. Voltage sensing device according to claim 1, wherein the voltage sensing device (1) is designed such that it can be easily attached to a cable terminal.
13. A cable accessory comprising the voltage sensing device according to claim 1.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| EP14187151.7A EP3002594B1 (en) | 2014-09-30 | 2014-09-30 | Voltage sensing device |
| EP14187151.7 | 2014-09-30 | ||
| PCT/US2015/052290 WO2016053790A1 (en) | 2014-09-30 | 2015-09-25 | Voltage sensing device |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CN106716148A CN106716148A (en) | 2017-05-24 |
| CN106716148B true CN106716148B (en) | 2020-02-21 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN201580052763.3A Expired - Fee Related CN106716148B (en) | 2014-09-30 | 2015-09-25 | Voltage sensing device |
Country Status (4)
| Country | Link |
|---|---|
| US (1) | US10338103B2 (en) |
| EP (1) | EP3002594B1 (en) |
| CN (1) | CN106716148B (en) |
| WO (1) | WO2016053790A1 (en) |
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| CN112236681A (en) * | 2018-06-08 | 2021-01-15 | 3M创新有限公司 | Impedance assembly |
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| DE102019211950B3 (en) * | 2019-08-08 | 2020-11-26 | Siemens Aktiengesellschaft | Measuring an electrical voltage on a metal-enclosed switching device |
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| GB2588631B (en) * | 2019-10-29 | 2022-03-23 | Tavrida Electric Holding Ag | Voltage sensor for electrical switchgear and electrical switchgear comprising same |
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| CN114487562B (en) * | 2022-04-06 | 2022-07-05 | 南方电网数字电网研究院有限公司 | Voltage measurement method and device based on dielectric constant correction |
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Also Published As
| Publication number | Publication date |
|---|---|
| US20170234908A1 (en) | 2017-08-17 |
| US10338103B2 (en) | 2019-07-02 |
| EP3002594A1 (en) | 2016-04-06 |
| WO2016053790A1 (en) | 2016-04-07 |
| CN106716148A (en) | 2017-05-24 |
| EP3002594B1 (en) | 2019-06-05 |
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